At the Water Quality Association’s (WQA) Mid-Year Leadership Conference in Chicago last October, a presenter raised the issue of the emerging contaminant, acrylonitrile, and the need for growing awareness among WQA members.[1] In contrast to most drinking water contaminants, removal of acrylonitrile from contaminated source water concerns largely the manufacturers of drinking water treatment units (DWTU). In addition, they are also concerned with not adding more of the contaminant to treated water because of any materials used in the design of these units.

Acrylonitrile is a colorless liquid with a strong onion- or garlic-like odor.[2] Ranking among the 50 highest-volume chemicals produced in 1999, 117 facilities released over 5.4 million pounds into the environment with 17.9 percent going into underground injection wells. Once in the environment, however, the chemical--especially when contacted with ultraviolet (UV) light--tends to break down rapidly. It has a half-life of five to 50 hours under such conditions.

A manufactured chemical, acrylonitrile is used to make plastics, synthetic rubber, elastomers, acrylic fibers and resins, i.e., acrylonitrile-butadiene-styrene (ABS). Since ABS materials are resistant to rust and corrosion and are relatively lightweight, they’re an attractive resin for pipe and housing construction and are commonly used in point-of-use DWTUs.

Health consequences Most information on the health effects of acrylonitriles is from occupational contacts. In the workplace, exposures are primarily via the respiratory route, where adverse health affects involving the nervous system (disorientation, headache, nausea, convulsions and paralysis) and lungs (throat irritation and breathing difficulties) are most common. Contact with the chemical can also illicit irritation or burns and blisters to the skin.

In addition to these acute effects, chronic exposures may also lead to a higher incidence of cancer. The U.S. Environmental Protection Agency (USEPA) has classified acrylonitrile as a Group B1 contaminant meaning that it’s a probable human carcinogen (cancer-causing agent). Although human data are inconclusive, animal studies have shown that acrylonitrile causes cancers of the stomach, brain and mammary glands, among others. Birth defects have been seen in animals and reproductive disorders have been realized through three generations in laboratory tests.

Exposure risks are difficult to extrapolate to humans, where personal characteristics can vary individual risks substantially. Children, however, appear to be much more sensitive to acrylonitriles since deaths have occurred in children in acute exposure compared to only minor symptoms in adults.

Waterborne exposure routes Acrylonitrile is highly soluble in water, therefore increasing the potential for source water contamination, especially near industrial manufacturing and disposal sites. Although it typically breaks down in about one to two weeks in water, it has been documented to persist in wells for up to a year following a spill. Little is known about the fate and transport of this chemical in various environments or the true risks of the waterborne route of exposure.

In addition to water, the general population may be exposed to acrylonitriles in plastic products. Regulatory safeguards are therefore in place to prevent consumption of acrylonitriles through consumer product usage. Many, if not most, DWTUs utilize ABS components that contact water during the course of water treatment. Typically, the concentration of acrylonitrile in ABS copolymers is about 30 to 50 parts per million (ppm). The amount suspected of leaching from the plastic product to the water supply is considered to be extremely low.[1]

Regulatory standards The USEPA regulates acrylonitrile under various acts including the Clean Air Act and the Clean Water Act. Maximum contaminant levels (MCLs) are set by the USEPA as the highest level of a contaminant allowed in drinking water. MCLs are designed to ensure that drinking water doesn’t pose either a short-term or long-term health risk. Although acrylonitriles have no MCL, federal health advisory levels are listed--by the USEPA--at different risk categories, i.e., 10-{6} = 0.06 parts per billion (ppb) or 10-{5} = 0.6 ppb. In addition, NSF/ANSI Standard 61 has a published value for acrylonitrile set at 0.6 ppb, which is based upon USEPA criteria and externally peer reviewed through CPHC--the Council on Public Health Consultants--and other groups. Further, the USEPA recommends that acrylonitrile levels in lakes and streams not exceed 0.06 ppb and any environmental release in excess of 100 pounds must be reported. In addition, the Occupational Safety and Health Administration (OSHA) limits exposure to 2 ppm over an eight-hour day and 40-hour week in the workplace while the National Institute of Occupational Safety and Health (NIOSH) limits acrylonitrile in air to an average of 1 ppm over a 10-hour period.

Testing protocols in DWTU standards differ from that of Standard 61 (see www.nsf.org/newsletters/regworld 01-2/ for a description of specific protocols), whereby many of the Standard 61 sections require an extended conditioning period; however, the overall goal is the same. In general, the test standards are aimed at ensuring materials in contact with drinking water don’t impart levels of extractable contaminants exceeding maximum drinking water levels (MDWLs) specified in the standard. These contaminants may be regulated or unregulated. Food-grade (FDA Title 21 CFR-compliant) ABS has been tested and certified extensively by NSF, WQA and UL as meeting DWTU standards.

Proposals & rebuttals

In January 2002, a balloted action was presented before the NSF Council of Public Health Consultants proposing, in part, a revision of the DWTU standards. These revisions would have changed the present extraction test level of 5 ppb (currently, an advisory concentration) to 0.6 ppb (a mandatory MDWL). Such a revision would have placed a marked burden on the DWTU industry where previous detection limits reportedly ranged between 1.0 ppb and 5.0 ppb--thus requiring re-testing of units containing ABS plastic to ensure compliance with a new, lower level.

Following the proposed MDWL of 0.6 ppb in the DWTU acrylonitrile standard, representatives from the domestic drinking water treatment equipment industry voiced the need for further discussions and review. In particular, discussions were requested regarding the technological and economical feasibility of current testing protocols used to evaluate DWTUs. The proposed requirement of 0.6 ppb was determined on the basis of NSF/ANSI Standard 61 safety levels but did not consider the variations in test protocols used in Standard 61 vs. DWTU testing procedures.

Conclusion Effective in 2003, the DWTU Standards adopted, through a deviation, an acrylonitrile MDWL of 6.0 ppb. The revised levels will officially be added to the standard at the next printing of the standards and all certified products must now meet this new level. Therefore, products in compliance with the previous advisory level would remain in compliance with the new MDWL. Sources claim that current studies being undertaken may even increase the MDWL above the current level, however, these results are not expected any time soon.

About the author Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on development of rapid methods for detecting human pathogenic viruses in drinking water. She holds a master of science degree in public health (MSPH) from the University of South Florida and doctorate in microbiology from the University of Arizona. Reynolds has also been a member of the WC&P Technical Review Committee since 1997.